15 November, 2022

The importance of soil and vegetation characteristics for establishing ground-nesting bee aggregations

 by Tsiolis et al.

A nest of a solitary ground-nesting bees with a
“chimney” extending from nest entrance.

The annual market value of animal pollination has been estimated at £180-442 billion worldwide. Ways to provide floral resources for pollinators are well developed; however, methods for provisioning areas for ground-nesting bees are poorly understood. This is a very important gap in knowledge if we consider that around 64% of approximately 20,000 known bee species are ground nesters.  Solitary bees need both flowers for food and a place to live, such as bare ground to nest in. The increasing number of studies highlighting the effectiveness of several ground-nesting bee species as crop pollinators suggest that we should focus on understanding their nesting needs and providing the appropriate nesting resources.

In this study, the nesting preferences of solitary ground-nesting bees were determined by creating eight 20m2 bare ground nesting plots at NIAB East Malling Research, UK. Nine soil parameters were measured along with recording the peak nest density of plots. The soil parameters were hydraulic conductivity (soil’s water absorbance rate), soil compaction (soil hardness), soil moisture, soil temperature, soil stoniness, soil organic matter, soil root biomass, soil texture and vegetation cover. Soil stoniness and soil temperature at 10cm depth were determined as favourable factors, whereas vegetation cover and hydraulic conductivity were determined as the non-favourable factors by ground-nesting bees for nesting.

This study provides novel insights into the habitat preferences of ground-nesting bees and shows how the creation of bare-ground plots can be used to enhance the populations of ground-nesting bee species. The findings shared here would underpin more general implications for the sustainable management of a largely overlooked group of bee species, which have a central role in food security.
 

26 October, 2022

By land and by tree: Pollinator taxa diversity of terrestrial and epiphytic orchids

 By Haleigh A. Ray & Jennifer L. Gillett-Kaufman

 
(L) An epiphytic Camylocentrum pachyrrhizum in Collier County, Florida.
Photograph by Haleigh Ray, and
(R) a terrestrial Habenaria sp. In Volusia County, Florida.
Photograph by Kirsten Work

With nearly 30,000 different species orchids are the second largest plant family. Despite this large number, there are still many questions about the pollination biology of orchids. These orchids can grow terrestrially like many other plants, or as epiphytes, where they will grow on another living host, most often the branches or trunk of a tree, without harming the tree. While many orchid pollinators are insects, there have also been birds and a single mammal species identified as successful pollinators. In this paper we review various pollination strategies that orchids use, and analyze a comparison between terrestrial and epiphytic orchids, including whether their growth type influences their pollinator diversity. Over 400 species of orchids and their documented pollinators were included from published literature, including orchids from 50 different countries.
Of the orchid species in this review, 55% were pollinated by bees and wasps, 20% by flies, 16% by butterflies and moths, 4% by beetles, and 3.5% by birds. When comparing the epiphytic orchids to the terrestrial orchids, we found that the bees and beetles pollinated more terrestrial taxa than epiphytic, while there was no difference from the other pollinators. Additionally, the terrestrial orchids were pollinated by more pollinator taxa than the epiphytes, suggesting that they have more diverse pollination strategies. With orchids facing threats from poaching, climate change, and habitat loss, learning more about their reproduction is crucial for ensuring their conservation.
 
Read the scientific publication in JPE!

26 September, 2022

Consequences of pollinator availability and effectiveness for pollen transfer in a gynodioecious seed crop system

 by R. Waytes, R. Cartar, S. Hoover

A leafcutter bee on canola

Pollen limitation can constrain the number of seeds that a plant sets, and therefore its reproductive success. For plants that depend on animal pollinators, the availability of pollen is determined in part by the availability of pollinators and their ability to effectively deposit pollen (i.e., their efficacy).

We studied pollinator visitation and efficacy in hybrid seed canola (Brassica napus) production fields in Alberta, Canada. These fields consisted of 1 m wide bays (lines) of ‘male’ flowers (hermaphrodites which act as pollen-donors) alternating with 6 m wide bays (lines) of ‘female’ flowers (hermaphrodites with induced male sterility). Honey bees (Apis mellifera) and alfalfa leafcutting bees (‘leafcutter bees’; Megachile rotundata), both introduced European species, are typically placed in the crop for pollination. Native pollinators, including bees and flies, may also contribute. We used a GoPro® camera targeted at an inflorescence of female flowers placed at 1 m distance from the observer to offer flowers to insects visiting the canola and record their responses. We examined how insects responded to female flowers and what behaviours affected pollen deposition. Additionally, we measured pollinator visitation to both male and female bays.

Most flower visitation in this system was by managed pollinators (honey bees and leafcutter bees), who were placed and maintained in the canola fields. Flies and native bees were present, but at much lower numbers. Honey bees and leafcutter bees tended to individually specialize on male or female flowers, and their unwillingness to move between bays represents a potential barrier to pollen transfer.

Female leafcutter bees deposited more pollen than honey bees or flies, although male leafcutter bees and honey bees deposited similar amounts. Bumble bees were similar to female leafcutter bees in pollen deposition, but their low presence in the canola fields implies low contributions to overall pollination. Pollen deposition increased with the amount of time a pollinator spent on a flower.

So what mattered in pollen deposition? Far and away, it was the sex of flower from which the pollinator moved: moving from a male flower transferred more pollen. Also important were pollinator identity (female leafcutter bees were the best) and time on flower (more time meant more pollen deposited). Pollen receipt is a confluence of three factors: from where, who, and how long.